Nitrogen oxides are at illegally high levels in many British cities and the government estimates this pollution is responsible for 23,500 premature deaths a year
Photograph: Ingo Wagner/Associated Press

Ninety-seven percent of all modern diesel cars emit more toxic nitrogen oxide (NOx) pollution on the road than the official limit, according to the most comprehensive set of data yet published, with a quarter producing at least six times more than the limit.

Diesel cars' emissions far higher on road than in lab, tests show

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Surprisingly, the tiny number of models that did not exceed the standard were mostly Volkswagens, the carmaker whose cheating of diesel emissions tests which emerged last year sparked the scandal. Experts said the new results show that clean diesel cars can be made but that virtually all manufacturers have failed to do so.

The new data, from testing industry leader Emissions Analytics (EA), follows the publication this week by the Department for Transport of emissions results for 37 vehicles, all of which emitted more NOx on the road than the official limit. But the new data covers more than 250 vehicles in more stringently standardised road conditions. EA found that just one of 201 Euro 5 diesels, the EU standard from 2009, did not exceed the limit, while only seven of 62 Euro 6 diesels, the stricter standard since 2014, did so.

Diesel cars must meet an official EU limit for NOx but are only tested in a laboratory under fixed conditions. All vehicles sold pass this regulation but, when taken out on to real roads, almost all emit far more pollution. There is no suggestion that any of the cars tested broke the law on emissions limits or used any cheat devices.

An ultra-low emission zone in central London from 2020 will levy charges on all but the cleanest vehicles. The Conservative candidate, Zac Goldsmith, said he would be immediately consulting on a more stringent zone which could be extended to outer boroughs. “Londoners are seeing their lives cut short because of the misleading emissions produced by some of the world’s biggest and most respected car brands.”

Goldsmith added that as mayor he would issue public smog alerts to give accurate information on air quality.

Caroline Pidgeon, the Lib Dem mayoral candidate, said: “The figures are exactly the reason why we need to speed up the introduction of the ultra-low emission zone so that it starts in 2018. Ultimately we will need to ban diesel vehicles from much of London and we need a mayor prepared to take these tough decisions and work with people to make these changes happen.”

“There is a growing worry about air pollution, but while some car manufacturers have been more proactive, others have done only the minimum,” said Nick Molden, the CEO of EA. “The point is diesels can be clean.”

Government passing the buck on air pollution, say campaigners

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EA claims to have tested the emissions of more cars driving on real roads than any other group in the world and has now published the NOx results for 263 models. The good performance of the VW models, which did not have cheat devices fitted, was surprising, Molden said: “It is hugely ironic.”

The EA analysis found that just one of the 201 Euro 5 diesels tested – a Skoda Octavia – did not exceed the official limit on the road. Over a quarter of the Euro 5s pumped out at least five times the official limit, including models from BMW, Range Rover, Mercedes, Nissan, Renault and Vauxhall.

Of the 62 Euro 6 models tested by EA, seven did not exceed the official limit in real-world driving: four Volkswagens, a BMW, an Audi and a Skoda. However, an Audi A8 and a Fiat 500X were found to emit more than 12 times the official limit, while a BMW X3, a Volvo S60 and a Vauxhall Zafira were among models emitting more than six times the official limit on the road.

The EA tests were all performed on the same route in south-west London, with the same drivers, at the same time of day and with the same load weight in the vehicles. Tests were only performed when the weather – temperature, rain and wind – was within certain parameters.

One leading respiratory expert said the emissions discrepancies shown in the DfT report released on Thursday amounted to “an unacceptable scandal”.

Sir Malcolm Green, a professor of respiratory medicine who founded the British Lung Foundation, said the revelations showed “appalling behaviour” by many major car firms. “This is a massive failure of public trust by these companies,” he said.

“It is well established that current levels of pollution are shortening people’s lives, on a population basis,” Green said. “This is a massive and deliberate deceit. It’s appalling behaviour by the car manufacturers involved.

“They were selling these cars on the basis that they were clean diesels. I find it shocking. The more we look into it, the more it looks like a widespread thing across many manufacturers. It’s outrageous and unacceptable.”

Asthma UK said two-thirds of asthmatics reported their condition being exacerbated by high levels of emissions. “People with asthma need accurate information about asthma triggers, including air pollution, to help them manage their condition,” said Dan Murphy, the head of external affairs for Asthma UK.

“So if they’ve got this level of misinformation it’s going to affect the choices they make. That is a concern for us.”

Steve Gooding, the director of the RAC Foundation, said “The [EA data] demonstrates that diesel cars can score well in real-world driving conditions. However, the star performers in the diesel category are few in number and these figures send out a strong message to several auto makers that they need to up their game.”

The Society of Motor Manufacturers and Traders, which represents the motor industry in the UK, said: “The differences between the results from official laboratory tests and those performed in the real world are well known, and industry acknowledges the need for fundamental reform of the current official test regime, which does it no favours.”

Unlike other parts of the world, European nations incentivised the use of diesel vehicles over the last 20 years because they emit less carbon dioxide per mile than petrol cars. Governments thought stricter regulation would sharply reduce NOx emissions, but carmakers found ways around the rules and governments failed to clamp down on the practices.

The EA data is available for free to the public as the EQUA index. Molden said there was understandably a great deal of confusion among car buyers: “But we’re able to deliver impartial and precise information to help them buy better.” He said future regulation, such as ultra-low emission zones, would mean people choosing the cleanest cars would avoid charges.

The index is overseen by a board of experts including Prof Helen ApSimon, at Imperial College London, and Dr Adam Boies, at the University of Cambridge. “The public can use it to avoid buying cars that are more harmful to human health,” said ApSimon. Boies added: “The index will enable us to track the industry’s effort to make meaningful reductions in noxious emissions.”